U.S. Pat. No. 3,825,509 describes an aqueous emulsion obtained by emulsifying an organic peroxide in an aqueous solution containing 1-5% by weight of polyvinyl alcohol and 1-6% by weight of polyoxyethylene sorbitan monolaurate. However, such emulsions lack physical stability and at organic peroxide concentrations higher than 19% by weight these emulsions become viscous and difficult to handle. U.S. Pat. No. 3,988,261 describes aqueous peroxide emulsions consisting of 30-75% by weight of an organic peroxide; an emulsifying amount of a water-soluble surfactant; and water. These emulsions are stable to freeze-thaw cycles and therefore the emulsions are generally frozen for transportation and subsequently thawed before use. It is stated that as a result these frozen peroxide emulsions are relatively safe and easy to handle and transport. It is mentioned that the safe handling of such emulsions is due in part to the fact that frozen emulsions offer a large self-contained heat sink because of a latent heat of fusion of the water component.
However, the use of such frozen emulsions has several disadvantages. Due to the fact that in actual practice large quantities of frozen emulsions are generally stored, if the frozen emulsion is exposed to a rapidly rising ambient temperature, the relatively large heat sink and the low heat conductivity of ice will initially give rise only to the melting of the outermost portion of the frozen emulsion. Because of the difference between the conductivity of the liquid emulsion and the frozen emulsion, the temperature of the small amount of liquid peroxide emulsion produced will rapidly rise. Under such circumstances the frozen emulsion will produce the uncontrolled decomposition of the peroxide rather than non-frozen, aqueous emulsions. In addition the frozen emulsion particles tend to aggregate, and as a result the size of the resulting particles will be considerably increased.
Furthermore, procedures, employing frozen emulsions require several additional steps which are undesirable in practical applications. Initially, the emulsion must be frozen. Then before it can be used, the emulsion is thawed. Such thawing procedures require the utmost care. In addition, in view of the general instability of peroxides, the thawed emulsions must be rapidly processed. If this is not possible, the activity of the thawed peroxide emulsion will decrease radially. Although frozen emulsions may be employed in this solid form, metering of solid substances is difficult to automate and the fusion of the emulsion particles may make it difficult to obtain the correct feed rate.
Conventional emulsions contain, in addition to peroxide, generally surfactants, protective colloids and water. The incorporation in these emulsions of additional substances such as alkanols and alkane diols is considered objectionable in view of the possible negative influence thereof on the peroxide and the resulting polymer. For example, it has been noted that the addition of 0.5% to 2% by weight of 2-ethylhexanol to di-2-ethylhexylperoxydicarbonate causes the active oxygen content to decrease by 30 to 40% after two months storage at 0.degree. C. For samples not containing the alcohol, the decrease in active oxygen content was 5%. Furthermore, alcohols may serve as chain transfer agents when utilized in (co)polymerization reactions of ethylenically unsaturated compounds and as a result cause a decrease in the molecular weight of the polymer.
German Patent Application No. 2,418,386 describes aqueous suspensions that contain 1-30% by weight of benzoyl peroxide, 1-30% by weight of surfactant and 10-80% by weight of an alcohol. However in a suspension, unlike an emulsion, the risk of alcohol diffusing in the peroxide is generally not expected. In addition, benzoyl peroxide is a member of a considerably stabler class of compounds than the present peroxides. German Patent Application No. 2,629,467 describes aqueous dispersions of solid oil-soluble radical initiators that are stable when stored at a temperature above -5.degree. C. and may contain substances that decrease the melting point. The present invention, however, relates to emulsions of organic peroxides that are generally unstable at temperatures greater than -5.degree. C.